Dyslexia affects the lives of millions of people world-wide and often has devastating psychological, social and educational consequences. It is also one of the most controversial topics in the fields of developmental neurology, psychology, and education. The controversy arises from the incomplete definition of the syndrome of dyslexia and from contradictory theories that surround its etiology.
A major difference between dyslexia and other reading disabilities is that, unlike dyslexia, other categories of reading failure can be predicted on the basis of neurological, intelligence, socio-economic, educational and psychological (motivational, emotional) factors known to adversely affect the reading process. If, for instance, a child has problems in one or more of the above-mentioned areas, he is expected to have reading problems. The extent of the reading disability is determined by the severity and number of factors that are involved.
In contrast, if a child has none of the above-mentioned problems, he is expected to be a normal reader. Children are presently classified as dyslexic when their failure to learn to read cannot be predicted by deficiencies in any of the known causes of poor reading. Psychological, socio-environmental, educational and intelligence factors do not cause dyslexia, although they can contribute to its severity or amelioration. The causes of dyslexia are unknown, and there is substantial disagreement on the definition of dyslexia. Lack of knowledge as to the causes of dyslexia has forced the adoption of definitions based on exclusionary criteria. The diagnosis of dyslexia by the use of exclusionary criteria delays diagnoses by at least 1.5 to 2 years after the beginning of school. This generally results in the development of psychological problems secondary to reading failure, and limited effectiveness of treatment following delayed diagnosis. Furthermore, children presently cannot be unequivocally diagnosed as dyslexics if they are:
(a) psychologically maladjusted prior to beginning schooling; PA1 (b) from a disadvantaged socio-cultural background; PA1 (c) educationally deprived; or PA1 (d) of low intelligence.
It is thus desirable to develop a definition that would identify dyslexics on the basis of positive behavioral, psychological and/or neurophysiological symptoms such as abnormal EEG or evoked potential and/or erratic eye movements. A major advantage of a positive definition of dyslexia is that it would make possible an unequivocal diagnosis in children from disadvantaged socio-cultural and educational backgrounds, as well as in children who are psychologically disturbed or of low intelligence.